Small computers such as "personal computers" ordinarily operate as a stand alone device, carrying out information processing based on programming and data stored locally on a floppy or hard disk or in semiconductor memory media. Data can be transferred among computers digitally by cables connected to input-output ports of the computers or to commercial telephone lines or other physical media following digital-to-analog conversion by modems. Computers also can be interconnected in a local area network (LAN), sharing common resources such as data bases, files and programming, and peripheral devices, e.g., printers. Accessing from one computer a resource of another computer on a common network is not done "transparently", i.e., a computer having a desired resource must be accessed before the resource associated with it is accessed. The user accordingly must have knowledge of the location of the resource on the Network.
For example, referring to FIG. 1, a plurality of terminals T are coupled through modems M to a network. Each terminal T comprises a personal computer PC and an optional telephone unit TEL to enable the user to carry out voice communications with other terminals on the line. The computers PC, which are controlled by a common operating system, such as MS-DOS, contain data, applications and peripheral devices, hereinafter collectively called "resources", that are accessible through operating system commands. An example is a floppy or hard disk drive unit DS residing at each computer PC.
Assume that a local computer contains two disk drive units DSA and DSB, a floppy disk drive and a hard disk drive. To copy all data stored on disk drive unit DSA to drive unit DSB, the operating system command in MS-DOS is:
copy DSA:*.* DSB:
Conventionally, the operating system enables multiple resources to be accessed by a computer. However, no sharing of resources among different computers is possible unless the computers are programmed to operate as "master-slave" units. Remote access software, such as "pcANYWHERE", by Dynamic Microprocessor Associates, Inc., is an example of commercially available software for this purpose. Resource sharing requires each computer on the Network to be loaded with, and executing, the remote accesses software.
Files can be transferred between computers using conventional file transfer software, such as "SMARTCOM", by Hayes Microcomputing, but file transfer requires operator attendance at each terminal.
The present invention is directed to a router that provides resource sharing among computers standing alone or residing in local area networks LANs without operator attendance at the "slave" terminal. Communications between computers is transparent, enabling the user to access distributed resources without knowledge of the locations of the resources on the Network.
The invention is carried out in the environment of ISDN. ISDN is a relatively newly developed and emerging field of telecommunications which integrates computer and communications technologies to provide, worldwide, a common, all-digital network. This is based, in part, on standardizing the structure of digital protocols developed by the International Telegraph and Telephone Consultative Committee (CCITT). Despite implementation of multiple networks within national boundaries, from a user's point of view there is a single, uniformly accessible, worldwide network capable of handling a broad range of telephone, data and other conventional and enhanced services. The invention, carried out on the ISDN, will enable terminal resources to be shared globally.
A complete description of the architecture of ISDN is beyond the scope of this specification. For details, and for an extensive bibliography of references of ISDN, see Stallings, ISDN: An Introduction, MacMillan Publishing Company, 1989. Copending application Ser. No. 976,923 and now U.S. Pat. No. 5,463,629, to Ko, entitled "Dynamic Channel Allocation Method and System for Integrated Services Digital Network," filed by the assignee of this invention, provides a background discussion of ISDN features that are germane to the present invention, and is incorporated herein by reference.
To establish communications between a host and the ISDN, an interface, or "relay", must be implemented to accomplish gateway functions, translating protocols used on dissimilar networks. A relay of a type termed a "bridge" forms interconnections at the data-link layer of the OSI Reference Model. A "router" functions at the network layer, and a "gateway" handles higher-level protocols.
An ISDN router, designated by R in FIG. 2, operates entirely in the digital domain, carrying out all necessary protocol conversion between the host network and ISDN. Details of the router R are given in copending application Ser. No. 094,144 and now U.S. Pat. No. 5,444,703, to Gagliardi et al., entitled "ISDN Interfacing of Personal Computers," filed by the common assignee on even date herewith and incorporated herein by reference.
Copending application Ser. No. 094,143 and now U.S. Pat. No. 5,442,630, to Gagliardi et al., entitled "ISDN Interfacing of Local Area Networks," filed on even date herewith and assigned to the common assignee, describes a router supporting interconnections among hosts on the ISDN to form a "virtual" LAN. A local area network, or LAN, provides a cluster of interconnected hosts (computers), or nodes, on a medium. Each node can communicate with every other node; the Network requires no central node or computer.
FIG. 3 depicts utilization of one type of router described in the aforementioned copending application (LAN connector) for interconnecting a number of hosts to form a virtual B-channel LAN. A variation, shown in FIG. 4, provides ISDN routers R to interconnect to LANs of a common type or of different types. In FIG. 5, a remote host H is connected to a pair of hosts residing on a LAN through first and second routers at the host and LAN branches of the ISDN. The host side router R1 is of a type described in the copending application entitled "ISDN Interfacing of Personal Computers." The LAN side router R2 in FIG. 5 is of a type described in the copending application entitled "ISDN Interfacing of Local Area Networks."
Copending application Ser. No. 094,115 and now U.S. Pat. No. 5,479,407, to Ko et al., entitled "Channel Utilization Method and System for ISDN", describes an ISDN router that dynamically allocates bandwidth by monitoring traffic at each destination queue and in response allocates or deallocates virtual B-channels. Bandwidth utilization is optimized by packaging data packets into trains that are transmitted to the destination when the train is completed and upon satisfaction of other conditions. Each train undergoes data compression by execution of a suitable compression algorithm.
Relays exist for allowing communication to an ISDN line. For example, U.S. Pat. No. 4,885,739 describes a message transport network at a central office, including gateways connected to a transport node controller or transport interchange supervisor to enable communication between internal processors. U.S. Pat. No. 4,821,265 describes a nodal architecture for a communication network including multiple processors for each node to carry out a Data Link Layer process on a D-channel message received through a bridge (termed a "gateway" in the patent). However, no prior art is known to enable ISDN users to share terminal resources, such as data storage disks, transparently from any terminal on the Network.